Electrostatic information storage



ELECTROSTATIC INFORMATION STORAGE Filed Dec. 6, 1954 4 Sheets-Sheet 1 I Fig.1.

14 1 logkc/s PULSE L l 11 STEPPED 3;?? 13 I- INVENTOAS F. c. WILLIAMS 'roM mmumzm me By G, a, no

MW, D -W ATTORNE Y5 April 12, 1960 F. c. WlLLl AMS Hm. I 2,932,763

ELECTROSTATIC INFORMATION STORAGE Filed Dec. 6, 1954 4 Sheets-Sheet 2 (a) BEAT Oscmumoru 171s (b) CONTROL GRID T (c) X- PLATES u 24 E (d) PICK-UP ELECTRODE 1) V 27 2s I STROBE TIME INVENTORS F. C. WILLIAMS 'I'OM KILBURU BY G. R. HOFFMAH M IQW W h' ATTORNEYS April 12, 1960 F. c. WILLIAMS ETAL 2,932,763

ELECTROSTATIC INFORMATION STORAGE Filed Dec. 6, 1954 4 Sheets-Sheet 3 36 VOLTAGE POSITV. 38 1 VOLTAGE /34 soulzcs VARIABLE vogAeE L S QEE -10- T g Q j so p IND/CAT R AMPL? INVENTORS I F. G. WILLIAMS v POM KILBURN G. R. HOFJMAN WNW ATTORNEYS April 12, 1960 F. c; WILLIAMS EI'AL 2,932,763

ELECTROSTATIC INFORMATION STORAGE Filed Dec. 6, 1954 4 Sheets-Sheet 4 To MESH 5'1 T eRm 31 gsglwron Kc/s PULSE 6 zeg p 33 5'0 Mc/s MC 5 GEN GEN B To osnii P A I4 I L L TES sTRoBEjfi DASH, .48 DOT 49 ERASE WRITE REA D 6 54 INVENTORS 'all-Ma To KM 3A. RI W B3; MM B wfilhk ATTORA/Efi Patented Apr. 12, 1960 2,932,7 3 I ELEC'IROSTATICINFORMATION STORAGE Frederic Calland Williams, Romiley, and Tom Kilbnrn and George Richard Hoffman, Manchester, England,

assignors toNational Research Development Corporattion, London, England Application December 6, 1954, Serial No. 473,360,.

Claims priority, application Great Britain December 11, 1953 10 ciainis." c i.s1 s;-s:s

The present invention relates to the, storage of information, particularly digital information, using a cathode ray tube, in which. the information is stored in the form of different charge, conditions'on elemental. areas of a charge-retaining storage surface within the tube.

In the specification of co-pending application Serial No; 50,136, for example, there is described a method of storage in which each digit interval (that is the time allotted' to the storageof a digit) is dividedinto two parts. During the first part theelemental area is-bombardeduwiththe cathode ray beam in order to read the information storedon the area by generating in a signal plate electrostatically coupled to the storage surface a signal representative of the state of charge of the area. The second part of each digit interval is allotted to modifying, when'required by the nature of the information to be stored on the elemental area, the state of charge left on that area after the bombardment thereof by the beam. The signal generated in the signal plate may be used to determine whether the state of'charge left on the area after the first bombardment is 'changcd'or not, thereby regenerating the charge condition which the area had before the bombardment. Alternatively the information read during-the first part of a digit interval may be fed to a computer andthe decision whether the. 40

area is to be bombarded during the second part of the digit interval or not may then be determined by a signal received from the computer. p

In the aforesaid prior specification the bombardments during thetwo parts of a digit'interval take place upon different parts ofithe storage surface: in ne example two adjacent areas'and'in another example 'are latively 2 is determined by the potential of an electrode in or near the surface and on the bombarded side thereof, the method comprising bombarding the area with the beam while applying to the said electrode a first potential or range of potentials, thereby producing on the area a charge representative of one digit, when required to store a differentdigit on the area carrying out a second bombardment of the area with-the beam while applying to the electrode a second potential or range of potentials different from the first potential or range of potentials,

thereby producing on the area acharge representative of the different digit, and, in order to read the stored information, bombarding the area with the beam Whilst applying to the said electrode the first potential or range of potentials, thereby generating in a signal plate capacitively coupled to the said surface a voltage representative of the digit stored on the area. i 1

The invention also provides a method of storing digital information upon an electriccharge-retaining storage surface in a cathode ray tube and of reading such'ihformation in which the potential to which an elemental 'area of the surface is charged upon bombardment ofthc area with the cathode ray beam is determined by'the potential of .an electrode in or near the surface and on the bombarded side thereof, the method comprising directing the cathode'ray beam 'successively upon a number of elemental areas on the surface, the beam being held directed upon each such areafor the duration of a digit interval, bombarding each area wit-hthe beam during a first part of each digit interval, While applying to the said electrode a first potential or range .of potentials, in

order to produceon the area a charge representative'of one digit and to generate in a signalplate capacitively coupled to the said surface a. voltage representative of the charge upon'the' area before the said bombardment thereof, and, when required to store a different digiton large area during the 'first part of the'digit interval and a small area within the outer boundaries of therelatively large area during the second part of the digit interval.- Sucharrangements havethe disadvantage that the el e mental area which bears the state of charge representing the information stored is not the whole digit area bombarded duringfa digit interval.

Since the digit areas (that is the areas that receive bombardment) have to, be spaced apart by a distance sufficient to prevent mutual' interference between adjacent elemental areas, it is obviously desirable that the 7 digit areas 'shou ld be as nearlyco-extensive as possible with the elemental areas,

The present invention. has for its principal object to provide an improved met-bod and'means for' storage of information in which each elemental areais co-ex'tensive with the corresponding :digit area," that is to say the elemental areawhich bears the'characteristic charge from which the read 'si'gnal'isTderived is .theonly area bom- 'barded during ,each' digit interval.

According'to the-present invention there isprovided a methodofstoring digital information-upon an electric chergeeretaining storageasurfaceuin iaycathOde rayf tube and ofead nadef rmati ns whichwthe potential to ud ii h .ielem ntal area of. the; -sur.face. -is charged upon bombardment of the areawithzthesathode ray beam the area, bombarding the area during a later part .of the digit interval while applying; to the electrode a second potential or range of potentials different from the first potential or range ofipotentials. The said electrode will be referred to. hereinafter for convenience as the mesh.

When the beam bombards the storage surface, secondary electrons are released from the area to the mesh until t the area assumes a potentialclose to that of the mesh and hence the charge assumed by the elemental area .jmoval of the cloud of electrons in the neighbourhood of the area). is generated in the signal plate when the beam next bombards'the area.- If, on the other hand, the area has been bombarded, as described, during thelater part.

of the digit interval, when next the area is bombarded by the beam a signal will be generated'in the signal plate. It? is immaterial whether the mesh potential during the first part of a digit interval is the higher or the lower. 7

When regeneration is required, the-signal generated in :the' signal plate during the first part of the-digit interval can 'be hsed'to determine whetherthe bombardment during the later part ofthe digit interval is to take placeor not and hence whether the charge left on the area during the first bombardment is to bechanged'or not.

If different steady potentials are applied to the mesh a difficulty arises because the change in potential has to be considerable,.for instance tensof volts, and the changes have to take place rapidly for high speed operation. The result is that large andsuddenvoltage changes are induced in the signal plate and are passed to the amplifier connected to the signal plate, where they tend to overload the amplifier and also to obscure the read signals generated in the signal plate. These large voltage changes cannot readily be filtered out.

In order to overcome this difficulty the effect required is produced by applying high frequency oscillations to' the mesh and to the control grid or cathode of the cathode ray tube, the relative phase of the two oscillations during the first and the later part of each digit interval respectively differing by about 180. The oscillation on the control grid or cathode is arranged to switchthe beam on and off. Consequently, when the two oscillations are in one phase relation the beam is switched on while the positive peaks of the high frequency oscillationare applied to the mesh and when the two oscillations are in the opposite phase relation thebeam is switched on' While the negative peaks .of the high frequency oscillation are applied to the mesh.

The required change in phase relationis conveniently obtained by feeding to the mesh and to the .control grid -or cathode two oscillations of slightly different frequency, the beats between the two oscillations having a period equal to the recurrence period of the digit intervals.

Although, as will be'evident to those skilled in the part, many ditferent forms of apparatus for carrying the .method of the invention into efiect can be devised, the

invention also provides a preferred form of such apparatus as set forth in appended claims.

The invention will be further described with reference to the accompanying drawings in which :Fig. l is a circuit diagram of a preferred form of apparatus according to the invention, 7 I

Fig. 2 contains waveforms present in the circuit of Fig. 1,

Fig. 3 is a circuit diagram illustrating the basic principles of the invention,

Fig. 14 is a circuit diagram showing one form that the pulse generator unit of Fig. 1 may take, and

'Figs. 5 and 6 are much enlarged viewsin front and side elevation respectively of a fragment of the cathode ray tube screen in Fig. 1.

Referring first to Fig. 3, a cathode ray tube 10 has a screen comprising an insulator 11 (much exaggerated in thickness), a mesh 12, and a pick-up plate 13. Electrons from a cathode 30 are formed intoa beam by an electrode system represented diagrammatically at 32 and strike the screen 11. The beam is normally switched'olf and can be switched onibyclosing a switch 39 to apply a suitable positive potential from a source 34 to a con- ,trol grid 31. A variable voltage source 35. coupled to a deflector plate 16 enables the cathode ray beam to be deflectedto desired positions on the screen 11. Two

different voltages 1 and 2 can be applied to the mesh 12 from sources 36 and 37 by operating a switch 38.

In operation, one digit (say 0) can be recorded upon a digit area selected by adjustingthe control of source 35 by momentarily closing the switch 39 while the switch 38 is set, as shown, to apply volt-agel to the mesh. The area bombarded then assumes a potential close to that of the mesh 12. In order to read the information stored on this area, the switch 39 is again momentarily closed with the switch 38 in the position shown, that is with voltage 1 on the mesh 12. Since the po tential on the area of the screen 11 bombarded will not be substantially changed by this 'operatiorna negligible .voltage change takes placein the pick-up plate 13 which is'coupled through an amplifier 40 to an indicator 41.

Thus the indicator 41 gives no indication and indicates that the stored digit is 0. r

In order to record a different digit (say 1) on a selected area, the switch 39 isv momentarily closed with the switch 38 set, as shown, to voltage 1. The switch 38 is then moved to its other position to put voltage 2 011 the mesh. 12 and the switch 39 is again momentarily closed.

The potential of the area bombarded then changes to a value close to voltage 2. In order to read the information stored on this area, the procedure is, as before, to close the switch 39 momentarily with the switch 38 in the position shown, namely with voltage 1 on the mesh. The effect will be to change the potential on the area bombarded from a value close to 2 to a value close to l and a corresponding voltage pulse is generated in the pick-up plate 13 and indicated at 41.

The operation described is obviously too slow for use in computers and a preferred form of apparatus suitable forhigh speed operation is shown in Fig. l in which like parts have the same reference as in Fig. 3.

In Fig. 1, oscillations of 5.0 and 5.1 mc./s. from a generator 14 are applied to the mesh 12 and the control grid 31 of the tube 10 respectively. A pulse generator unit 15 is adapted to generate'positive-going dot and dash-extension pulses which are locked to the 100 kc/s. beat between the 5.0 and 5.1 mc./s. oscillations and applied to the control grid of the tube 10 .to bias the control grid to a potential at which the cathode ray beam is switched on during the positive peaks of the 5.1 mc./s.

A stepped waveform as shown at- (c) in Fig. 2 is applied from a stepped saw-tooth oscillation gfilj erator 33 synchronised by pulses from 15 .to X'deflecting plates 1 6.' Each of the horizontal portions of-t he waveform (c) defines an elemental area on which a digit is stored and its duration t defines a digit interval. 7 v The 100 kc. /s. beat oscillation between the two radio frequencies from the generator 14 is shown at (a) in Fig. 2. The pulse generator unit 15 is capable of generating dot pulses 17 which are applied continuously to the control grid and dash-extension pulses 18 which are applied selectively to the control grid. The bright-up waveform ofFig. 2(b) represents the waveform required in order to store dots and dashes (or 0 and 1) on alternate elemental areas. 7 V

The pulses from generator unit 15 are locked instep with the 100 kc./s. beat between the oscillations from 14 and with the stepped waveform (c) in Fig. 2 in such a.manner that the dot pulses 17 occur during the first cluding anamplifier comprising valves 19 and 20 and the pulse generator unit 15 to5the control grid of the tube 10; This loop circuit maybe constituted as described in United States.app1ication, Ser. No. 124,192, filed October 28, 1949, by Frederic C. Williams et :11. Thus as shown in Fig. 4, the anode of valve 20 is connected to the input of a circuit comprising four valves 42, 43,344 and 45. Pulses from a pulse generator 46 locked in synchronism with the beat frequency .of the oscillator 14 are applied to synchronise the stepped, saw-tooth generator. 33, a strobe pulse generator 47 generating the pulses of Fig. 2(a), a dash-extension pulse generator 48 generating the pulses'18 in Fig. 2(b), and a dot pulse generator 49 generating the pulses. 17 inFig. 2(b). In order to write a 1 a suitably timed negative pulse is applied to a write terminal 50. In order to write a 0" over an existing 1 a suitably timed negative pulse is applied to an erase terminalSl. Output may be obtained for example from a read terminal 52. .The circuit of Fig. 4.is described in more detail; in. US. application Ser. No. 124,192 referred to above.

The amplifier shown inFig. 1 contains means for suppressing the radiofrequency oscillations from the generator 14 applied to the mesh 12. The means, in the embodiment shown, arean acceptor circuit 21 and a rejector circuit 22 both tuned to 5 mc./s. and a 1r filter 23 connected between the valves 19 and 20-and designed to-suppress the SmcJs-frequency. 1 v

' the full value of potential.

' these charge conditions are to be read (using the waveform of Fig. 2(b)) and regenerated, when the first pulse 17 occurs the potential of the area bombarded has to be raised because during the previous, scan the area was last bombarded during the later part of the digit interval and was therefore left at the lower potentiala This pulse, therefore, gives rise on the pick-up plate 13to a positive pulse 24 in Fig. 2(d The first pulse .18 occurs during the later part of the first digit interval andthe reduction in potential of the area bombarded gives rise to a negative pulse 25 on the pick-up plate.

.When the second pulse 17 of Fig.- 2(b) occurs the area bombarded is at the higher potential since during the previous scan of this-area no bright-up pulse Ill-occurred. Consequently only a small negative pulse 26 is produced in the pick-up plate. a r

Pulses from the strobe pulse generator, of Fig.4 select from the waveform of Fig},2 (d),.only the parts" occurring during the strobe pulses, Thus'estrobe pulse 27 selects a positive, pulse which when fed to the control grid of the valve 42 in vFig. 4 releases a dash-extension 1 pulse 18 which is applied tothev control grid 31 of the tube 10, thus regenerating the original charge condition The mesh as shown in FigsL S and 6 consists of a single set of parallel conducting strips 54. The strips should be as narrow as possible consistent with their ohmic resistance being lowenough. Their spacing should be such that the spot produced thereon by the cathode ray beam covers at least three of the parallel strips. Alternatively one another to form a grid may be used.

Although preferred ways of carrying out the invention have been described, it may be carried out in many other ways. A

According to one such way, a sinusoidal oscillation of, for example, 100 kc./s., is applied to the mesh, the beam being stationary for a digitinterval which includes at least a substantial part of a positive and a negative halfcycle of the oscillation, and being moved forward between digit' intervals. In order to record one digit the beam is switched on or intensified only during the first part of the digit interval, while either the positive or the negative half-cycle is driving the mesh. In order to record another digit, the beam is switched on or inon the area. 7 The strobeipulse ZSstr bes only the small negative pulse 26 and this has no effect on the circuit 15 of Fig. l and. consequently. a dash-extension pulse is not, passed to the control grid of the tube 19. Here,,again,' therefore, the originalstate of charge is regenerated When the beam. is switched on by the peaks of the high frequency oscillation for the duration of a dot 'or a dash interval, the potential ofthe area bombarded-approaches its full value (that which. it would assume ifthe bombardment continuedindefinitely) asymptotically- Tor a given duration of the bombardment the closeness of approach ticn such as'is usually required, the area does not assume The potential attained in or-' der to represent one digit will, therefore, not be constant but will depend tosome extent on Whether the, sameor a plied. to themesh during the wholeofeach quarter cycle 1 of the'beat frequencypreceding the peak value thereof; It is clearlygundesirable thattherboa should be switched on after-these eak value Even th gh the earlier part of thequ'arter cycle referred to does not have much effect in comparison with the effect produced by the later part, nevertheless it does make a contribution to the final potential attained by the area.

Instead of applying the high frequency oscillations continuously to the cathode ray tube and biasing the tube into operation by means of the dot and dash extension pulses as described, the tube may be biased permanently into a condition tobe switched on by high frequency oscillations applied to its control grid or cathode and the high frequency oscillations may be applied to the control grid or cathode in bursts at the times of occurrence of the dot pulses and (when required) of the dash extension pulses. The high frequency oscillations may be applied continuously to the mesh.

The mesh is arranged close to the bombarded surface of a charge-retaining screen and may be in contact the surface. A suitable screen provided with a mesh is described in United'States patent application Serial bio. 473,359, filed on the sarnedate as the present application.

tensified, or kept switched on 'or intensified, during the second part of the digit interval, while the negative or positive half-cycle, respectively, is driving the mesh. Whether the beam is switched on or intensified during the second part of a digit interval may be determined by the signal generatedin the pickup plate, when regeneration-is required, or 'by'a write signal.

As already explainedf'means must be provided for suppressing the kc./s.- component in the output of the i pick-up electrode in order to avoid overloading the amthe bridge circuit to'avoid the use of elements, such as ceramic capacitors, which may introduce non-linearity.-

It is also importantto arrange, in all embodiments, that the impedance of the mesh to ground should be low.

' Another Way of carrying out the invention is to use two oscillations of the same frequency which is many times the digit recurrence'frequency; for example the frequency may be S mc./s.. One of the oscillations is ap-.

plied to the mesh and the other to a beam intensity control electrode, for instance the cathode. During the first part of each dig-it interval the oscillations are in at least approximately the same phase and during'thef other part of each interval at least approximately in anti-phase. A Write signal or, for regeneration, a signal from the pick up plate is applied to determine whether the oscillation is applied to the cathode during the'later part of each digit interval or not, the cathode ray beam being arranged to be cut off in the absence of the oscillation. The oscillations may be appliedto the cathode through two gating pentodes in parallel, oscillations in one phase being applied to the control grid of one and in the opposite phase to the control grid'of the other. Square waves of digit recurrence frequency and opposite phase are applied to the respective suppressor grids.

The 5 mc./ s. oscillations may be suppressed in the circuit between the pick-up plate and the amplifier as de scribed with reference to Fig. 1.

The present invention can be used in conjunction with that set forth in United States application Serial No.

1 273,114, filed February 23, 1952 by G. I. Thofnal et al.,

in which after reading the information on an elemental area the beam is moved backwards to modify (when required) the charge on an elemental area previously read.

Moreover the clamping and integrating circuits set forth inUnitedStates application Serial No; 175,794, filed July 25, 1950, by F. C.' Williams et al., now Patent No. 2,727,988," issued December 20, 1955, are advan tageously used in conjunction with the present invention.

We claim:

1. A method of storing digital information upon an electric charge-retaining storage member in a cathode ray tube, the storage member having an electron-permeable electrode upon the side thereof bombarded by the cathode ray beam of the tube, the method comprising the steps of storing a first digit on one elemental area on said member by bombarding'the area with the cathode ray beam while applying a first potential to said electrode,

and storing a second digit on another elemental area on H said member by first bombarding said other area with said beam while applying said firstpotential to said electrode and subsequently bombarding said other area with said beam while applying to said electrode a second potential difierent from said'first potential.

2. A method according to claim 1, wherein said potentials are oscillatory. e

3. Apparatus for storing digital information comprising a cathode ray tube, electron beam-producing means,

beam-deflecting -means, beam-intensity control means and acharge-retaining storage member in said tube, said member having a storage surface positioned to be bombarded by said beam, an electron-permeable electrode on the side of said member facing said beam-producing means, a stepped saw-tooth oscillation generator,

means coupling said generator to said beam-deflecting means, pulse-generating means, means generating two different potentials, circuits connecting said pulse-gencrating means to said beam intensity control means and said potential-generating means to said electronpermeable electrode respectively, and switching means in at least one of said circuits responsive to information to be stored.

4. Apparatus according to claim 3, wherein said pulsegenerating means generate two sets of recurrent pulses, one set occurring during an early part of each step of the Y waveform from said saw-tooth generator and the other set occurring during a later part of each said step, and wherein said switching means are in the circuit connected to said pulse-generating means to permit and prevent the application of the second-named set of pulses to said beam-intensity control means.

5. Apparatus for storing digital information comprising a cathode ray tube, electron beam-producing means, beam-deflecting means, beam intensity control means and a charge-retaining storage member in said tube, said memberhaving a storage surface positioned to be bombarded by said beam, an electron-permeable electrode on the 'side of said member facing said beam-producing means, oscillation generating means coupled to said electron-permeable electrode and to-said beam-intensity condiffering by approximately 6. Apparatus for storing digital information comprising a cathode ray tube, electron beam-producing means, beam-deflecting means, beam intensity control means and a charge-retaining storage'member in said tube, said member having a storage surface positioned to be bombarded by said beam, an electron-permeable electrode on the side of said member facing said beam-producing means, oscillation generating means coupled to said electron-permeable electrode and to said beam-intensity control means and applying to said electrode and control means respectively two oscillations of frequencies differing from one another by an amount which is a small fraction-of the frequency of each of said oscillations.

7. Apparatus according to claim 6, comprising pulsegenerating means coupled to said beam-intensity control means and to said oscillation-generating means to lock the pulses generated by the pulse-generating means to the beat frequency between said two oscillations.

8. Apparatus according to claim 7, comprising "a stepped saw-tooth oscillation generator coupled to said beam deflecting means and to said pulse generating means to lock the stepped waveform from said saw-tooth generator to said beat frequency.

9. Apparatus according to claim 8, wherein said pulse generating means generates two sets of recurrent pulses,

switching means whereby charges on said surface are regenerated.

References Cited in the file of patent UNITED STATES PATENTS 2,454,410 Snyder Nov. 23, 1948 2,589,460 'luller Mar. 18, 1952 2,639,425 Russell et al. May 19, 1953 2,671,607 Williams'et a1. Mar. 19, 1954 2,706,246

Kleniperer Apr. 12, 1955 

